I run a 175 front, 170 rear and about 140 mid position on a triplet. No reason not to have differing lengths depending on rider. Crank arm shorteners are also a choice, but are likely to be less than the 165 that you mentioned. The shorter crank arm also makes it so that the seat does not have to be lowered as far, or allows a shorter rider to ride on the back if the saddle is at the bottom of its possible height.